Electrophoresis is an analytical technique for separating and identifying charged particles, ions, or molecules. Electrophoresis involves the imposition of an electric field in order to move a charged species in a medium. The molecules to be separated are placed in wells of a gel medium which comes in contact with a buffer contained in a tank. The most often studied species are bio-macromolecules, such as proteins and nucleic acids (e.g. RNA molecules and DNA fragments), which are usually polyelectrolytes. However, electrophoresis can be used to separate any charged materials including various cells, bacteria and viral materials.
At a fixed pH and ionic strength, a given polyelectrolyte acquires a certain number of net charges. Such particles are surrounded by counter-ions and have various charges and sizes (volume and shape) which affect movement.
Molecules are differentiated by their different mobility's under an applied electric field. The mobility variation derives from the different charge and frictional resistance characteristics of the molecules. The more charged and streamlined the molecules, the faster their movement. The positively charged molecules will move to the negative electrode (cathode) and the negatively charged molecules will move to the positive electrode (anode).
When a mixture containing several molecular species is introduced to an electrophoretic separation medium and an electric field is applied, the different charged components migrate at varying speeds, producing the resolution of the mixture. The location of each of the separated bands depends on the mobility of each component, on the interaction of the polyelectrolytes with the surrounding medium via the influence of pH, ionic strength, ion type and on whether the medium is a buffered solution of ions, polymeric solution, or gel such as a cross-linked gel. The most frequently used gel media are based on polyacrylamide (known as PAGE) and agarose gels.
Vertical electrophoresis apparatuses use acrylamide gels for the separation of proteins and small nucleic acid molecules. These systems include a set of vertically disposed glass plates within which the gel is held and an upper and a lower buffer chamber. The use of two separated vertical buffer chambers presents a number of inconveniences. For instance, the buffer volume needed to fill both chambers is usually large. Additionally, during the vertical electrophoresis process, the upper chamber often leaks. If the upper chamber is not refilled quickly, the results may be distorted and valuable samples could be lost. Moreover, uniform heat distribution across the gel is necessary for even banding separation and reproducibility. However, the use of two vertical isolated buffer chambers may result in a non-uniform heat distribution across the gel.
Prior art horizontal electrophoresis apparatuses are designed for easy separation of large nucleic acid molecules on agarose gels. These apparatuses, however, require a large volume of buffer in order to completely submerge the gel.
It is an object of the present invention to benefit from the advantages of both the vertical and horizontal gel apparatuses. The electrophoretic tank of the present invention is designed for horizontal gel electrophoresis, utilizing both agarose gel for nucleic acid electrophoresis and polyacrylamide gel for small nucleic acid molecules and protein electrophoresis.
A further object of the present invention is to provide an electrophoresis gel tank that is portable, and is easy and safe to use.
The electrophoresis device disclosed in the invention may be particularly used with a gel device as described in WO 02/37094, which describes a gel device that overcomes the inconveniences involved with vertical electrophoresis. The gel device comprises a gel cassette with two open legs to allow ionic communication with the buffer in the chambers. The gel cassette may include an agarose gel, a polyacrylamide gel, a gradient gel or a hybrid agarose-polyacrylamide gel precasted.